Thermal cracking heater



United States Patent [72] Inventors Wilson J. Weber, ,lr.

Groves;

James L. Terry, deceased, late of Nederland, Tex., by Lola Irene Terry, Executrix, Neder land, Tex.

June 6, 1969 Continuation of Ser. No. 651524735519, "Wrflllfifilll Dec. 22, 1970 Jefferson Chemical Company Inc. Houston, Tex.

a corporation of Delaware [21] App]. No. [22] Filed [45] Patented [73] Assignee [54] THERMAL CRACKING HEATER 3 Claims, 3 Drawing Figs.

[52] U.S.Cl. 165/74; 277/98 [51] lnt.Cl. F28d 1/06 [50] Field ofSearch.. 165/52,53, 11, 162, I57, 73,74

[56] References Cited UNITED STATES PATENTS 1,013,745 1/1912 Clark 2 7 7L9 2,149,954 3/1939 Brock..... 165 /1 57; 2,639,928 5/1953 Robbins V 2 7 7/ 99 3,305,002 2/ I 967 Leonard, Jr. et al l65/74X Primary Examiner-Robert A. OLeary Assistant Examiner-Theophil W. Streule Attorneys-Carl G. Ries, John R. Kirk, Jr. and H. G. Jackson ABSTRACT: In thermal cracking heaters having a plurality of tubes a therrnowell housing attached to the tubes protrudes through the heater wall. The annular opening surrounding the housing is covered by a plate oriented about the housing and held in slidable contact with the heater wall such that the thermowell may move in response to heat changes and the opening remain effectively closed.

HE ATER WALL 22 2 HEATER TUBE flNSULATION THERMAL CRACKING HEATER CROSS-REFERENCE TO COPENDING APPLICATIONS This application is acontinuation of Ser. No. 654,524 filed Jul. 19, 1967, now abandoned, for Apparatus for Closing an Aperture."

BACKGROUND OF THE INVENTION 1. Field of the Invention v This invention pertains to a thermal cracking heater in combination with a device useful for closing an annular opening about a thennowell housing which allows the housing to move within the heater causes the thennowell housing to protrude even further through the opening in the heater wall.

2. Description of the Prior Art Y Y i 1 By closing the aforementioned annular opening, it prevents outside air from being drawn into the-heater while it is in operation which causes an inefficiency due tothe necessity of heating this outside air. It is necessary, however, that the aperture-in the wall of the thermal cracking heater be fairly large, usually 4 to 6 inches in diameter, dueto-thetendency of the thermowell housing to misalign itself with the axis of the aperture due to the sagging of the housing when the heater is at its operating temperature, usually above 1,600l F. It was previously the practice to caulk the aperture with an asbestos wicking or similar material to close the annular opening. This was unsatisfactory since the thermal expansion of the-heater tubes and the thermowell housing itself with consequent sagging would cause the packing to be pushed out of the annular opening or otherwise crushed by the sagging housing. This had the effect of not closing the aperture at all. Also, when the heater was taken out of operation and the tubes cooled, the sagging thermowell housing would pull the calking material into the vessel. This caused a maintenance problem in that when the heater was taken out of service and cooled, it was necessary for workmento enter the heater and cleanup the calking material which hadfallen to the inside floor of the vessel. Since the heaters operate for relativelyshort periods of time between maintenance shutdowns, this cleanup problem reocc'urs frequently. Therefore, calkinghas been an unsatisfactory solution to the problem of keeping this aperture closed during the operation of the heater. 1

It is an object of this invention to provide an improved thermal cracking heater which incorporates an apparatus for closing the annular opening in a heater wall through which a thermowell housing protrudes which allows -a cycle of heater operation from an inoperative, or cold, state through an operating, or hot, state and back to the inoperating state without necessitating the maintenance of the apparatus to keep the aperture effectively closed for subsequent cycles.

It is another object of this invention to provide an improved thermal cracking heater which incorporates an apparatus which, when effectively closing the aperture in a heater wall, will not restrict longitudinal movement of a protruding thermowell housing, butat the same timewill reorientitself relative to the heater wall to compensate. for misalignmentof the protruding thermowell housing, thus closing the'opening both during and after movement of the housing. 1

Other objectives of this inventionwill occur to thoseskilled in the art through the examination of this specification and are intended to be included herein.

SUMMARY. oaras mvenriou I The objectives of this invention areaccomplished by orienting about the perimeter of a protruding thermowell housing a plate which is sufficiently large to cover the aperture in the either be a 0ne-piece member with a hole therein to allow the protruding thermowell housing to freely move back and forth in response to temperature change or it may be a plurality of pieces which when situated and joined about the thermowell housing accomplishes the same end result. The plate is juxtaposed the wall and held in slidable contact with the wall of the heater by an appropriate biasing means such as springs or set bolts carried at the other end by a rigid member fixably attached to the wall of the heater such that the plate is between the rigid member and the wall. The means exerts a force upon the plate urging it against the wall of the heater while still allowing the plate to slide when the protruding housing sags,

becoming misaligned with the aperture in the heater wall. To accomplish this the plate should be of sufficient size that it overlaps the aperture even when the plate has moved with the sagging thermowell housing. When the heater is taken out of operation and the protruding thermowell housing withdraws toward the heater wall due to contraction of the heater tubes,

the hole will remain effectively covered. Thus, the prior necessity for maintenance is eliminated, resulting in a substantial savings of labor and material.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Thermal cracking heaters are widely used in industry to effect cleavage of carbon to carbon bonds of saturated apparatus of this invenhydrocarbons and to dehydrogenate hydrocarbon molecules to increase the unsaturation in the hydrocarbon chains through the application of heat. This is normally done in a gasfired heater with the hydrocarbon feedstock being cracked passing through a plurality of tubes connected by return bends such that the gas passes through the tubes in a series. The heat causes the molecules to break down to the desired unsaturated molecule during the time in which the gas is inthe heater. In order for there to be efficient cracking of the feedstock, it is necessary to control the temperature within the heater and consequently the temperature of the feedstock as it passes through the cracking tubes of the heater.

The temperature of the feedstock in the tube, 10 is usually measured through the introduction of a thermocouple in a thermowell 12 into the gas'stream as it passes through the tubes. This thennowell 12 is passed through a thermowell housing 14 and through a nozzle 16 welded to the return bend 18 of the tube 10. The thermowell housing I4 protrudes through an aperture 20 in the heater wall 22, creating an annular opening in the wall. The thermocouple well 12 is at tached, usually by a flange 24, to the thermocouple well housing 14.

' -When the heater isput into service and the temperature rises, the tube 10 expands, causing the thermowell housing 14 to move longitudinally of its axis and hence. protrude further through the aperture 20 in the wall 22 of the heater. In addiaperture 20 in the wall 22 of the heater creates an annular opening which is desirably covered throughout the cold to hot to cold cycle of the thermocracking heater. The practice of I this invention accomplishes this desired result of. keeping the annular opening covered throughout the operation cycle of the thermal cracking heater. While there may be a slight invasion of outside air around the cover, the amount is appreciably reduced from that previously experienced. In the practice of this invention, a plate 26 is in juxtaposition with the surface of the heater wall 22. The plate 26 has an opening of the same configuration of the thermowell housing 14 and is sized such that the thermowell housing 14 may freely move longitudinally therethrough. lf the plate 26 is to be installed at the time the cracking heater is assembled, the plate may be of one-piece construction. However, it is within the scope of this invention for the plate to be later installed in a plurality of pieces which, after being oriented around the perimeter of the existing thermowell and substantially juxtaposed the wall 22 of the heater, are then welded or otherwise joined to form a unitary plate covering the annular opening in the heater wall.

The plate 26 is heldin slidable contact with the wall 22 by a bias means, such as a plurality springs 28, which contacts the plate 26. Springs may be held in alignment by a lug 30 attached to plate 26, around which the end of the spring 28 contacting the plate 26 is orientated. The other end of the compressed spring 28 is orientated about a lug 32 and engages the surface of a rigid restraining-member 34, which is substantially parallel to the wall 22 of the heater and is rigidly attached thereto by a strut 36 or other appropriate means. The restraining member, such as a strap 34, is located adjacent to plate 26 sufficiently to compress the spring 28 exerting a force on the plate urging it against the heater wall 22 such that longitudinal movement of the thermowell housing 14 does not push the plate 26 from the heater wall 22. However, when the thermowell housing 14 sags and becomes misaligned with the aperture in the heater wall 22, the plate 26 will slide along the heater wall 22 such that the annular opening remains effectively closed by the plate 26.

The use of the above embodiment of this invention effectively closes'the thermowell housing openings in heaters, both during and after movement of the housing. Thus, the necessity of repacking these openings after each heater cycle is eliminated. This substantially reduces the necessity for expenditures on maintenance for this purpose. At the same time the openings are effectively closed during heater operation so outside air is not admitted in appreciable quantities to the interior of the heater, thus causing a-t'hermal inefficiency in the operation of the heater. I

It will be understood that various changes in the details, materials and arrangements, of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art without departing from the principle and scope of the invention as expressed in the appended claims:

it is claimed: 7

1. In a thermal cracking heater comprising a plurality of cracking tubes enclosed in a vessel, the tubes having a thermowell housing rigidly attached thereto. the housing protruding through an opening in a wall of the vessel and movable with respect to the wall, the improvement for effectively closing the opening through which the housing protrudes which comprises:

a. a, plate overlapping the opening having a hole therein and oriented about a perimeter of the housing and juxtaposed the wall;

b. at least one rigid member adjacent the plate and connected to the wall with the plate located between the rigid member and wall; and

c. a bias means carried by the rigid member for urging the plate in slidable contact with the wall; whereby the opening remains effectively closed during and after movement of the protruding member.

2. The improved thermal cracking heater of claim 1 wherein the bias means is a plurality of helical compression springs, one end of the spring contacting the plate and the other end contacting the rigid member.

3. The improved thermal cracking heater of claim 1 wherein the rigid member is a strap carried adjacent the plate by attachment to one end of a strut the other end of which strut is attached to the heater wall. 

